1. Field of the Invention
The present invention relates to instruments and methods for carpal tunnel release and, more particularly, to instruments and methods for minimally invasive carpal tunnel release wherein the transverse carpal ligament is accessed via a relatively small size incision and is divided with the assistance of endoscopic visualization.
2. Brief Discussion of the Related Art
Carpal tunnel syndrome is a commonly occurring medical condition arising from compression of the median nerve passing through the carpal tunnel of the wrist. Carpal tunnel syndrome is associated with various problematic symptoms including numbness, tingling, loss of sensation, pain which may be localized to the hand and which may radiate to the elbow, shoulder or neck of the patient, reduced grip strength, loss of muscle function, muscle atrophy, and loss of sleep due to nocturnal symptoms.
Various conditions may cause and/or aggravate carpal tunnel syndrome including non-specific flexor tenosynovitis, aberrant anatomy, injury, infection, inflammatory disease, metabolic disorders, intraneural hemorrhage, intrinsic enlargement of the volume of anatomical structures within the carpal tunnel, extrinsic compression of anatomical structures within the carpal tunnel, strenuous use of the hand and wrist, and repetitive motion of the hand and wrist. Carpal tunnel syndrome is one of the most common repetitive use injuries encountered in working adults and is being encountered with increasing frequency in younger age groups. Carpal tunnel syndrome oftentimes occurs bilaterally in a patient.
The carpal tunnel is defined by a concave arrangement of the wrist bones spanned on the volar or palmar aspect of the wrist by the flexor retinaculum, an essentially rigid ligament also known as the transverse carpal ligament. A distal portion of the ligament attaches to the hook of the hamate and to the ridge of the trapezium. A proximal portion of the ligament attaches to the pisiform and to the scaphoid tubercle. The transverse carpal ligament may be considered to define the roof of the carpal tunnel, with the floor and sides thereof being defined by the concave arrangement of the wrist bones. The carpal tunnel is a narrow space of essentially fixed size through which numerous important anatomical structures pass including the median nerve and various tendons. The median nerve passes through the carpal tunnel from the forearm and branches out distally to provide sensory enervation to the thumb, index finger, middle finger, and a portion of the ring finger. A motor branch of the median nerve supplies the thenar muscles that control movement of the thumb into opposition with the other fingers of the hand. The flexor digitorum superficialis tendons and the flexor digitorum profundis tendons pass through the carpal tunnel and are covered by a common synovial sheath. The flexor pollicis longus tendon passes through the carpal tunnel and is contained in its own synovial sheath. The synovium promote gliding of the tendons in conjunction with flexion and extension of the fingers. The median nerve is located in the carpal tunnel just under the transverse carpal ligament and over the synovial sheath containing the flexor digitorum tendons. In some atypical cases, an anomalous motor branch of the median nerve is present in the carpal tunnel or in the transverse carpal ligament.
Other important and sensitive anatomical structures or tissue in the vicinity of the carpal tunnel include the ulnar and radial arteries, the superficial palmar arterial arch, the ulnar and digital nerves, palmar aponeurosis, palmaris longus, abductor pollicis, and flexor carpi radialis. In addition to defining the roof of the carpal tunnel, the transverse carpal ligament defines the floor of the Guyon tunnel, which has the palmar carpal ligament as its volar boundary. The ulnar nerve and ulnar artery pass through the Guyon tunnel. The ulnar artery and nerve lie superficial to the transverse carpal ligament within the deep fascia overlying the transverse carpal ligament along the volar or palmar aspect of the wrist. The superficial fascia, in turn, overlies the deep fascia along the volar or palmar aspect of the wrist. Distal and proximal flexion creases are present in the skin along the volar aspect of the wrist, and the deep and superficial fascia are more tightly interconnected to one another at these flexion creases than are the deep and superficial fascia along the volar aspect of the forearm. The distal flexion crease normally demarcates the proximal boundary of the transverse carpal ligament. The distal boundary of the transverse carpal ligament is normally demarcated by Kaplan's cardinal line which courses from the hook of the hamate to the ulnar base of the thumb.
Non-surgical treatments for carpal tunnel syndrome, including rest, immobilization and anti-inflammatory medications, are not successful in relieving symptoms in a high percentage of cases. Consequently, surgical treatment known as carpal tunnel release, wherein the transverse carpal ligament is divided, transected or severed, is the treatment of choice in many cases of carpal tunnel syndrome. By completely severing the transverse carpal ligament, additional space is provided in the carpal tunnel to relieve pressure on the median nerve while retaining essentially normal wrist function in the patient.
Carpal tunnel release has traditionally been performed as an open surgical procedure requiring a long, deep incision through the skin and underlying anatomical structures or tissue extending from the wrist to mid-palm in order to expose the transverse carpal ligament. In open procedures, therefore, it is ordinarily necessary to divide or incise the palmaris brevis muscle, palmar fascia, thenar and hypothenar muscle fibers, fat and nerve fibers. There are many drawbacks to open surgical procedures for carpal tunnel release including considerable post-operative pain, increased risk of infection, long recovery times in which use of the hand is greatly curtailed, the need for the patient to wear immobilizing devices such as splints, unsightly scarring, loss of grip and pinch strength, the potential for inadvertent injury to nearby anatomical structures such as the palmar cutaneous nerve, and losses due to missed work. It is not unusual for patients recovering from open carpal tunnel release surgery to be unable to engage in normal employment or other routine activities for up to four to six weeks. The drawbacks associated with open carpal tunnel release surgery tend to be exacerbated in procedures involving palmar incisions on account of the highly specialized and sensitive nature of the skin and anatomical tissue in the area of the palm. However, any incision in the wrist at or close to a flexion crease is undesirable. Incisions that cross a flexion crease may result in undesirable complications including undesired tension on the incision line and hypertrophic scar formation. Incisions at or close to a flexion crease also result in greater pain for the patient due to this area being an anatomical joint subjected to frequent movement.
Some open surgical procedures for carpal tunnel release avoid a palmar incision by gaining access to the transverse carpal ligament from a transverse wrist incision proximal to the carpal tunnel. However, such procedures typically involve “blind” cutting of the transverse carpal ligament, thusly presenting a greater risk of inadvertent injury to nearby important anatomical structures as well as the risk that the transverse carpal ligament will not be completely severed. Moreover, in surgical procedures where a deep incision, even a transverse one, is made in the volar aspect of the wrist through the skin and underlying tissue, there is still a heightened risk of inadvertent injury and other complications for the patient because of the specialized and sensitive important anatomical structures and tissue in this area of the wrist.
It has been proposed to perform carpal tunnel release as a minimally invasive or endoscopic surgical procedure in which the transverse carpal ligament is accessed and severed using instruments introduced through a relatively small size incision and assisted by remote or endoscopic visualization. Minimally invasive carpal tunnel release provides many advantages over open surgical procedures including smaller incisions with less trauma and scarring for the patient, less pain and shorter recovery times for the patient, reduced risk of infection, the ability for the patient to begin using the hand and to return to employment and other normal activities sooner after the surgery, and a reduction in the need for immobilizing devices such as splints. Various instruments and methods for minimally invasive carpal tunnel release are represented by U.S. Pat. No. 5,968,061, U.S. Pat. No. 5,578,051 and U.S. Pat. No. 5,366,465 to Mirza, U.S. Pat. No. 5,908,431 and U.S. Pat. No. 5,730,749 to Battenfield, U.S. Pat. No. 5,651,790 and U.S. Pat. No. 5,458,611 to Resnick et al, U.S. Pat. No. 5,356,419, U.S. Pat. No. 5,346,503, U.S. Pat. No. 5,318,582 and U.S. Pat. No. 5,029,573 to Chow, U.S. Pat. No. 5,325,883 to Orr, U.S. Pat. No. 5,323,765 to Brown, U.S. Pat. No. 5,282,816 and U.S. Pat. No. 5,269,796 to Miller et al, U.S. Pat. No. 5,273,024 to Menon et al, U.S. Pat. No. 5,089,000, U.S. Pat. No. 4,963,147 and U.S. Pat. No. 4,962,770 to Agee et al, and by Okutsu et al in “Endoscopic Management of Carpal Tunnel Syndrome”, Arthroscopy: The Journal of Arthroscopic and Related Surgeries, Vol. 5(1), pages 11-18 (1989). Despite the benefits of minimally invasive or endoscopic procedures, prior instruments and methods for endoscopic carpal tunnel release have all too frequently resulted in various complications including injury to the superficial palmar arch, tendon lacerations, nerve injuries, incomplete release of the transverse carpal ligament, recurrence of symptoms, hematomas, and reflex sympathetic dystrophy. In many prior methods of endoscopic carpal tunnel release, the median nerve cannot be identified endoscopically with confidence or certainty, thereby creating reluctance on the part of many surgeons to perform carpal tunnel release as a minimally invasive procedure despite the benefits to be derived therefrom.
The minimally invasive procedure described in the Okutsu et al article is a single portal technique that involves forming an incision at the forearm, but still close to the flexion creases, inserting an obturator through the incision and into the carpal tunnel from the radial side of the palmaris longus tendon, removing the obturator and inserting a tube or sheath through the incision and into the carpal tunnel, and advancing an endoscope in the sheath to visualize the median nerve, flexor tendons and transverse carpal ligament. The sheath has a beveled distal end and is transparent to allow the endoscope to visualize the operative site through the wall of the sheath. Since the endoscope is not introduced until after formation of the incision, insertion of the obturator into the carpal tunnel and then insertion of the sheath into the carpal tunnel, the Okutsu et al procedure involves blind insertion of various instruments into the carpal tunnel and presents various opportunities for unintentional injury to critical anatomical structures before endoscopic visualization is established. Before the transverse carpal ligament is severed in the procedure described in the Okutsu et al article, the endoscope and sheath are removed and reinserted into the carpal tunnel on the ulnar side of the palmaris longus tendon. In a modified version of the procedure, the endoscope is initially inserted on the ulnar side of the palmaris longus. A hook knife is introduced into the carpal tunnel along the ulnar side of the sheath, and the median nerve is protected merely by retracting it away from the knife using the sheath. The knife is moved proximally to cut the transverse carpal ligament from its distal edge to its proximal edge, and the endoscope is simultaneously moved proximally within the sheath to visualize the cutting. The cutting performed with the knife is essentially freehand since the knife, and the sheath for that matter, are free to rotate or otherwise deviate out of position. It is thusly difficult to control the depth of the cut as well as the cutting location on the ligament. The ability to protect the median nerve depends on being able to hold the sheath in a position where it retracts the nerve away from the knife. Given the small size of the carpal tunnel, even small positional deviations of the instruments risk injury to important anatomical structures. It is also possible in the Okutsu et al procedure for the endoscopic image to be distorted due to visualization through the curved clear wall of the sheath. Furthermore, the need to move two separate instruments, i.e. the knife and the endoscope, independently but at the same time makes execution of the Okutsu et al procedure awkward and difficult as well as increases the potential for positional deviations of the instruments.
Another single portal endoscopic procedure in which the transverse carpal ligament is cut from distal to proximal and instruments for use in such procedure are exemplified by the Orr patent (U.S. Pat. No. 5,325,883). Orr provides a cannula for receiving an endoscope and a knife together therein. The cannula is a cylindrical tube, preferably made of metal, having an open proximal end and a closed blunt distal end defined by a convex distal end surface in union with the outer circumference of the tube. The cannula has a single slot therein beginning at its open proximal end and extending to its closed distal end. The slot allows the knife to access the transverse carpal ligament for cutting and allows the endoscope to visualize the cutting procedure from within the cannula. In the method of carpal tunnel release described by Orr, a transverse skin incision is made in the wrist 1 cm proximal to the volar flexion crease, and the incision is deepened by blunt dissection. A series of dilators of increasing diametric size are consecutively passed through the incision and into the carpal tunnel to create space for the cannula. An elevator is passed into the carpal tunnel and is used to separate the synovium from the underside or deep surface of the transverse carpal ligament. After these steps have been completed, the cannula is introduced into the carpal tunnel with the slot directed against the underside or deep surface of the ligament, and thereafter the endoscope is inserted in the cannula to visualize the ligament. Accordingly, all of the steps performed prior to introduction of the endoscope are performed blindly and unassisted by endoscopic visualization. After the distal margin of the ligament is identified using a hooked probe inserted in the cannula, the knife is inserted in the cannula and used to cut the ligament from its distal edge to its proximal edge while being visualized with the endoscope. Orr shows there to be a considerable amount of unoccupied space within the cannula when the endoscope and the knife are received together therein such that the endoscope and the knife are each free to move or deviate out of position within the cannula. Extension of the knife blade from the slot to cut through the ligament the proper depth is not controlled other than by the visualization provided by the endoscope. Moreover, the thickness of the slot is shown as being many times larger than the width of the knife blade such that the location of the knife blade within the slot width and, therefore, the cutting location on the ligament, is also not controlled other than by endoscopic visualization. In addition, it is difficult in the Orr procedure, and in other procedures that utilize a cannula or sheath of uniformly round external cross-section, to maintain alignment of the knife with a desired cutting location on the ligament because the uniformly round external cross-section of the cannula makes it especially prone to rotate. Despite the knife blade being contained in the slot while cutting the ligament, the lack of positional control over the instruments makes the cutting performed in the Orr procedure very similar to freehand cutting.
The endoscopic methods and instruments of the Agee et al patents (U.S. Pat. Nos. 4,962,770, 4,963,147 and 5,089,000) also relate to single portal carpal tunnel release involving distal to proximal cutting of the transverse carpal ligament. Agee et al provide a probe including a hollow sheath having a lateral aperture and having a closed blunt distal end terminating at a flat, angled distal end wall. A working tool comprising a pivotable cutting blade connected to a hollow shaft is received in the probe, the shaft being incrementally movable longitudinally within the probe via operation of a trigger grip to pivot the blade from a position where the blade is enclosed within the probe to a position where the blade is radially extended from the probe to project through the lateral aperture. A sight tube of an optical system is received in the shaft of the working tool, and is extended from a distal end of the shaft to provide visualization through the lateral aperture in the probe. The method of carpal tunnel release disclosed by Agee et al involves forming an incision proximal to but in close proximity to the carpal tunnel, continuing the incision through the deep fascia and the finger flexor synovium, and placing the wrist in extension to expose the proximal entry into the carpal tunnel, all of which steps are performed blindly since the probe and sight tube are not yet employed in the procedure. After the proximal entry into the carpal tunnel has been exposed, the probe is inserted through the incision and moved through the carpal tunnel to the distal edge of the transverse carpal ligament. The sight tube within the probe allows visualization of the anatomy within the carpal tunnel through the lateral aperture. The blade is extended from the lateral aperture to enable contact with the distal edge of the transverse carpal ligament. In order to cut the ligament from distal to proximal, the entire probe, with the working tool and sight tube received therein, is moved proximally. The cutting movement is repeated from distal to proximal as many passes or times as necessary to obtain complete division of the ligament. However, since the entire probe is moved from distal to proximal for each cutting movement or pass, it is difficult to return the probe to its previous distal position in order to obtain an endoscopic view of the cut already made in the ligament and/or to continue the cutting movement along the previously established cutting line. The instrumentation provided by Agee et al is bulky, difficult to maneuver with precision or accuracy, and provides limited endoscopic visualization through the lateral aperture of the probe.
The Menon et al patent (U.S. Pat. No. 5,273,024) pertains to a single portal endoscopic surgical procedure for carpal tunnel release in which an obturator is introduced in the carpal tunnel via a wrist incision, and is then removed and replaced with a series of increasingly larger dilators to prepare a space for insertion of a cannula/obturator assembly. The cannula/obturator assembly comprises a cannula of D-shaped interior cross-section and an obturator received within the cannula. The cannula has a closed blunt distal end and has a longitudinal slot extending from a point adjacent the distal end to a point adjacent an open proximal end of the cannula. After the distal end of the cannula/obturator assembly has been placed approximately at the distal margin of the transverse carpal ligament, the obturator is removed from the cannula and an endoscope is inserted axially in the cannula to provide visualization of the transverse carpal ligament via the slot. Accordingly, the Menon et al procedure entails blind insertion of various instruments into the carpal tunnel prior to establishment of endoscopic visualization. The Menon et al procedure further entails retracting the endoscope proximally within the cannula so that room is created in the cannula distal of the endoscope for accommodation of a knife used to cut the transverse carpal ligament. The knife is maneuvered into the slot in the cannula at an oblique angle distal of the endoscope. The knife is moved distally along the cannula to cut the transverse carpal ligament from proximal to distal and, in order to visualize the cutting procedure, the endoscope must be moved distally within the cannula to follow behind the knife. A standard needle inserted in the palm at the distal border of the ligament serves as a marker for visualization by the endoscope to prevent the surgeon from cutting too deeply into the palm. In order to inspect the median nerve endoscopically, the entire cannula must be rotated so that the slot faces the median nerve.
A further alternative single portal endoscopic surgical procedure for carpal tunnel release and instruments therefor are embodied in the Mirza patents (U.S. Pat. Nos. 5,968,061, 5,578,051 and 5,366,465). The instruments disclosed by Mirza include a cannula having an open blunt distal end and a slot extending the length of the cannula, an obturator for being received in the cannula and having a rib for mating engagement with the slot, an endoscope for being received in the cannula, and a knife blade for being mounted to the distal end of the endoscope. The Mirza procedure involves making an incision in the palm, deepening the incision to expose the palmar fascia, identifying the distal edge of the transverse carpal ligament and dividing it for approximately 5-6 mm, dividing the palmar fascia longitudinally, and exposing the transverse carpal ligament, all of which steps are performed without endoscopic visualization. Thereafter, the hand is secured in hyperextension, and a dissector inserted through the incision is used to dissect the transverse carpal ligament from the synovium. The dissector is withdrawn and the cannula having the obturator received therein is advanced along the path previously established by the dissector, which step is again performed without endoscopic visualization. The obturator is then withdrawn from the cannula and replaced with the endoscope for visualization of the transverse carpal ligament. Once the transverse carpal ligament has been identified, the endoscope is withdrawn from the cannula and replaced with the same or a different endoscope that has the knife blade mounted thereto, the knife blade slidably engaging in the slot in the cannula. The endoscope with the knife blade mounted thereto is advanced in the cannula, and the knife blade is used to cut the transverse carpal ligament under endoscopic visualization. Because the endoscope and knife blade are attached to one another in fixed relative positions, the field of endoscopic view is also fixed in relation to the knife blade and the cutting performed therewith on the ligament. Upon completion of cutting, the endoscope is removed and replaced in the cannula by an endoscope without a knife blade in order to inspect the ligament and median nerve, which requires that the cannula be rotated to afford a broader field of view. The Mirza procedure is disadvantageous for its blind insertion of instruments, its limited field of endoscopic view prior to, during and subsequent to the cutting procedure, the need for insertion and withdrawal of many instruments, the lack of protection for the knife blade as the scope is distally advanced within the cannula prior to actual cutting, and the need for securement of the hand in hyperextension. In addition, even a small size palmar incision is undesirable given the specialized nature of the palmar tissue and the presence of critical anatomical structures in the area of the palm.
The Chow patents (U.S. Pat. Nos. 5,029,573, 5,318,582, 5,346,503 and 5,356,419) relate to a dual or two portal endoscopic surgical procedure for carpal tunnel release and to instruments therefor. The instruments utilized in the Chow procedure include a sheath, a trocar, and a plurality of cutting instruments. The sheath is an elongate tube having an open proximal end, an open beveled distal end, and a slot extending the full length of the tube. The slot mates with a prominence on the trocar, which slidably fits within the sheath, and also provides access to the operative site for the cutting instruments inserted in the sheath. The cutting instruments include a probe knife, a triangular knife and a retrograde knife. The procedure is initiated by forming an entry portal or incision through the skin and subcutaneous tissue of the wrist, followed by a longitudinal cut of the fascia to expose the ulnar bursa and flexor tendons. The sheath, with the trocar disposed therein, is inserted in the incision and is advanced distally beneath the transverse carpal ligament. Following this step in the procedure, the patient's hand is secured in hyperextension. Following hyperextension of the hand, the sheath and trocar are together advanced further distally to exit the hand through an exit portal or incision in the palm. The trocar is then withdrawn from the sheath. All of the steps performed up to this point are performed blindly and without endoscopic visualization. An endoscope is then inserted into either of the open distal or proximal ends of the sheath, and the probe knife is inserted into the end of the sheath opposite the endoscope. The probe knife is used to locate the distal or proximal edge of the transverse carpal ligament via the slot in the sheath and is used to make an initial stab cut in the edge of the ligament. The probe knife is withdrawn and replaced in the sheath by the triangular knife, which is used to cut the mid-section of the ligament. The triangular knife is withdrawn and the retrograde knife is inserted into the sheath. The retrograde knife is used to form a cut joining the stab cut to the mid-section cut to complete division of a distal or proximal portion of the ligament depending on whether the stab cut originated in the distal or proximal edge of the ligament. The remaining distal or proximal portion of the ligament is divided in a similar but reverse manner after removing the endoscope and inserting it into the opposite end of the sheath. In the Chow procedure, the location of the entry and exit portals and the path for blind advancement of instruments between these portals are determined from external anatomical landmarks. Undesirable complications may ensue in patient's with internal anatomical anomalies, such as unusual anatomical location of the superficial palmer arch artery or unusual positioning of the motor branch of the median nerve. Moreover, given the small confined space in which critical anatomical structures are located in the wrist, undesirable complications may result where the instruments deviate even a small amount from the prescribed path. Because the hand is secured in hyperextension, the median nerve and other important anatomical structures are at increased risk of injury since they too are held in an immovable position. Furthermore, it is difficult in the Chow procedure to accurately position each of the several cutting instruments at the proper location so that each of the separately formed cuts in the ligament combine to form a continuous complete cut through the ligament. Additional drawbacks of the Chow procedure are that two portals are required and these are undesirably located in the volar aspect of the wrist and in the specialized tissue of the palm. In the Chow procedure as well as in other endoscopic procedures that utilize an incision in the palm and/or an incision in the volar aspect of the wrist, the location(s) of the incision(s) gives rise to various disadvantages including increased pain and longer recovery times for the patient, higher risk of inadvertent injury to the patient, and greater risk of complications. The need for multiple separate cuts and cutting instruments in order to effectuate a complete cut of the transverse carpal ligament in the Chow procedure increases the cost of instrumentation for the procedure and also extends the duration of the procedure. Surgical procedures of longer duration translate into greater cost but even more importantly place the patient at greater risk.
The Miller et al patents (U.S. Pat. Nos. 5,282,816 and 5,269,796) and the Resnick et al patents (U.S. Pat. Nos. 5,651,790 and 5,458,611) relate to instruments and methods for two portal endoscopic surgical procedures for carpal tunnel release which, like the Chow procedure, require an entry portal in the wrist and an exit portal in the palm determined from external anatomical landmarks. In discussing the Chow procedure, Miller et al and Resnick et al consider it a drawback of the Chow procedure to retract the flexor tendons toward the radial side after incising the volar antebrachial fascia to expose the flexor tendons. Miller et al and Resnick et al believe that retraction of the flexor tendons places undue traction upon both the ulnar and median neurovascular structure and results in an increased incidence of postoperative median and ulnar nerve neuropraxiae. In addition, Miller et al and Resnick et al believe that the Chow procedure places the ulnar neurovascular structures at risk by requiring deep dissection into the carpal tunnel. In the procedure described by Miller et al, after the volar antebrachial fascia is incised to expose the flexor tendons, a cannula/obturator assembly is placed under the transverse carpal ligament using direct visualization, and gentle pressure is used to “walk” the assembly under the ligament. Miller et al provides a slotted cannula having an open distal end with a blunt, flat distal end surface, and provides an obturator for insertion in the cannula to form the cannula/obturator assembly. The slot in the cannula extends practically the entire length of the cannula. In reality, the cannula/obturator assembly is “walked” under the ligament in essentially a blind fashion due to the limited field of direct view distal to the assembly and due to there being no provision for endoscopic visualization at this point in the procedure. The obturator is removed from the cannula and replaced with an endoscope only after the cannula/obturator assembly has exited the palm at the exit portal, the endoscope being used to visualize the transverse carpal ligament through the slot. Cutting of the ligament involves multiple separate cuts and cutting instruments similar to the Chow procedure. The instruments and method of the Resnick et al patents are similar to those of the Miller et al patents. In addition to blind insertion of the cannula/obturator assembly through the carpal tunnel, the procedures described by Miller et al and Resnick et al have many of the same disadvantages as the Chow procedure.
The Brown patent (U.S. Pat. No. 5,323,765) describes a dual portal endoscopic procedure for carpal tunnel release that is essentially a modification of the Chow procedure and describes instruments for use in the procedure. As in the Chow procedure, the procedure of Brown involves blindly passing a cannula/obturator assembly under the transverse carpal ligament from an entry portal in the volar aspect of the wrist and through an exit portal in the palm. The cannula of the cannula/obturator assembly has an open, blunt distal end and a single longitudinal slot extending nearly the entire length of the cannula. The entry portal is located 0.5 to 1.5 cm proximal to the distal flexion crease and, preferably, is located in the proximal flexion crease. Prior to the cannula/obturator assembly being inserted in the entry portal, retractors are inserted to expose and raise the fascia, and an elevator is inserted to dissect the synovium from the transverse carpal ligament. After the distal end of the cannula has exited the exit portal, the obturator is removed from the cannula and an endoscope is introduced in the distal end of the cannula. The procedure is therefore performed blindly up to this point and gives rise to the disadvantages associated with blind entry into the carpal tunnel and blind insertion of instruments therein. A hooked knife introduced in the proximal end of the cannula is used to divide the transverse carpal ligament from distal to proximal in one continuous motion as the endoscope is simultaneously moved proximally within the cannula to follow the knife. Like some of the other endoscopic procedures discussed above, the Brown procedure is disadvantageous not only for its blind procedural steps but also for its palmar and wrist incisions, its need for separate instruments to be introduced in opposite ends of the cannula, its lack of positional control over the instruments in the carpal tunnel and over the cutting location on the transverse carpal ligament, its limited field of endoscopic view, and its need for simultaneous movement of the knife and the endoscope from opposite ends of the cannula.
The Battenfield patents (U.S. Pat. Nos. 5,908,431 and 5,730,749) pertain to instruments for use in dual portal endoscopic carpal tunnel release. The instruments disclosed by Battenfield include a cannula, preferably made of stainless steel, having an open diametrically narrowing distal tip terminating at a flat distal end surface and having a slot extending almost the entire length of the cannula. Other instruments disclosed by Battenfield include an obturator and a rasp for being received in the cannula. The rasp has a toothed segment that extends through the slot in the cannula. Battenfield mentions that an endoscope can be placed in the cannula but does not disclose that any other instrument can be present in the cannula along with the endoscope.
As seen from the above, prior methods of endoscopic carpal tunnel release propose to introduce instruments under the transverse carpal ligament in the subligamentous plane between the transverse carpal ligament and the flexor tendon synovial sheath. The insertion of instruments in the subligamentous plane between the transverse carpal ligament and the flexor tendon synovium sheath in endoscopic carpal tunnel release procedures is made more difficult due to the fact that wrist anatomy imparts an upward slope to the subligamentous plane in the distal direction. Conventional dilators and other conventional instruments used to enter the carpal tunnel in prior endoscopic carpal tunnel release procedures have distal end configurations which make it difficult to guide the instruments to follow the upward slope of the subligamentous plane. When these instruments are forwardly or distally advanced toward or beneath the transverse carpal ligament in a straight horizontal path or plane, the instruments commonly become obstructed, snagged or trapped in or by the synovium. In addition to increasing the complexity of the procedure and inflicting trauma on the patient, instruments that are obstructed, snagged or trapped by or in the synovium provide a poor vantage point for reliable endoscopic visualization of anatomical structures in the carpal tunnel because the clarity of the endoscopic image viewed through the synovium is distorted or impaired. Furthermore, some of the synovium will remain attached to the underside of the transverse carpal ligament which impairs endoscopic visualization of the ligament and the ability to identify the ligament with confidence.
In view of the deficiencies of prior instruments and methods for endoscopic carpal tunnel release, a need exists for improved instruments and methods for endoscopic carpal tunnel release which allow access to the carpal tunnel to be gained via a single portal located in the volar aspect of the forearm in an anatomically safe area, a considerable distance away from the flexion creases and other critical and sensitive anatomical structures and tissue in the more anatomically complex area of the wrist, which avoid a palmar incision as well as a wrist incision, which avoid the blind entry and insertion of instruments into the carpal tunnel, which allow introduction of a cannula into the carpal tunnel without an obturator or trocar disposed in the cannula, which enable entry into the carpal tunnel along the subligamentous plane between the transverse carpal ligament and flexor tendon synovium sheath, which provide enhanced endoscopic visualization, which provide a broader field of view of the operative site via an endoscope received in a cannula and without requiring that the cannula itself be rotated, which allow critical anatomical structures to be identified by endoscopic visualization with greater confidence and certainty, which provide improved positional stability of the instruments in the carpal tunnel while allowing relative displacement of adjacent anatomical structures, which avoid the need for securement of the wrist in hyperextension, which provide greater control and guidance over cutting of the transverse carpal ligament including the cutting location on the ligament as well as the depth of cut, which enable constant endoscopic visualization of the cutting procedure as well as improved visualization in the direction of cutting, which protect or shield the cutting blade when not intentionally deployed for cutting the transverse carpal ligament, which better ensure that the transverse carpal ligament will be completely divided, which avoid freehand cutting of the ligament, which increase the safety of endoscopic carpal tunnel release, which reduce the duration of endoscopic carpal tunnel release procedures, and which reduce the potential for surgeon error.